ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-13-9745-2013 Contact freezing: a review of experimental studies Ladino Moreno L. A. https://orcid.org/0000-0002-4941-7945 1 2 Stetzer O. 1 Lohmann U. https://orcid.org/0000-0001-8885-3785 1 Institute for Atmospheric and Climate Science, ETH Zurich, Universitätstrasse 16, 8092, Zurich, Switzerland now at: the Department of Chemistry, University of Toronto, Toronto, Ontario, Canada 02 10 2013 13 19 9745 9769 Copyright: © 2013 L. A. Ladino Moreno et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/13/9745/2013/acp-13-9745-2013.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/13/9745/2013/acp-13-9745-2013.pdf

This manuscript compiles both theoretical and experimental information on contact freezing with the aim to better understand this potentially important but still not well quantified heterogeneous freezing mode. There is no complete theory that describes contact freezing and how the energy barrier has to be overcome to nucleate an ice crystal by contact freezing. Experiments on contact freezing conducted using the cold plate technique indicate that it can initiate ice formation at warmer temperatures than immersion freezing. Additionally, a qualitative difference in the freezing temperatures between contact and immersion freezing has been found using different instrumentation and different ice nuclei. There is a lack of data on collision rates in most of the reported data, which inhibits a quantitative calculation of the freezing efficiencies. Thus, new or modified instrumentation to study contact nucleation in the laboratory and in the field are needed to identify the conditions at which contact nucleation could occur in the atmosphere. Important questions concerning contact freezing and its potential role for ice cloud formation and climate are also summarized.

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